The present invention relates to a method for providing enteric coating on solid dosage forms and aqueous coating compositions therefor.
As is well known, certain solid dosage forms are desired to be disintegrated only when they arrive at the intestinal canals upon oral administration and they are imparted with enterosoluble property by providing so-called enteric coating on the surface.
Known enteric coating compositions in the prior art are, for example, prepared by dissolving certain cellulose derivatives such as cellulose acetate phthalate, hydroxypropylmethylcellulose phthalate and the like in a suitable organic solvent to form an organic solution.
These enteric coating compositions in the form of organic solutions have several defects. For example, in the first place, they are undesirable because of the relatively high production cost due to the use of large volumes of organic solvents. Further, there can be problems from the standpoints of safety and environmental pollution since the use of an organic solvent is not free from the danger of fire or explosion in the course of the coating process and emission of the vapor of the organic solvents to the atmosphere causes a difficult problem of environmental pollution. In addition, any traces of the organic solvents remaining in the coating layer on the solid dosage forms are undesirable in consideration of possible toxicity of them.
It is therefore an important problem in the pharmaceutics to develop an aqueous enteric coating composition with wide versatility for various kinds of solid dosage forms and free from the above described problems in the prior art compositions of organic solution type for enteric coating.
Recently, several methods have been proposed for providing enteric coating on solid dosage forms by use of aqueous coating compositions (see, for example, Japanese Patent Publication No. 53-12569 and Japanese Patent Kokai No. 53-96314) but these methods have also some problems of their own.